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Versions: (draft-krishnan-6man-maxra) 00 01 02 03

IPv6 Maintenance                                             S. Krishnan
Internet-Draft                                                    Kaloom
Updates: 4861 (if approved)                                  J. Korhonen
Intended status: Standards Track                                Broadcom
Expires: January 4, 2018                                  S. Chakrabarti
                                                                Ericsson
                                                             E. Nordmark
                                                         Arista Networks
                                                          A. Yourtchenko
                                                                   cisco
                                                            July 3, 2017


        Support for adjustable maximum router lifetimes per-link
                        draft-ietf-6man-maxra-03

Abstract

   The neighbor discovery protocol specifies the maximum time allowed
   between sending unsolicited multicast Router Advertisements from a
   router interface as well as the maximum router lifetime.  It also
   allows the limits to be overridden by link-layer specific documents.
   This document allows for overriding these values on a per-link basis.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 4, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Relationship between AdvDefaultLifetime and MaxRtrAdvInterval   3
   4.  Updates to RFC4861  . . . . . . . . . . . . . . . . . . . . .   4
   5.  Host Behavior . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   IPv6 Neighbor Discovery relies on IP multicast with the expectation
   to be efficient with respect to available bandwidth and to avoid
   generating interrupts in the network nodes.  On some datalink layers
   multicast may not be natively supported.  On such links any possible
   reduction of multicast traffic will be highly beneficial.
   Unfortunately, due to the fixed protocol constants specified in
   [RFC4861] it is difficult to relax the multicast timers for neighbor
   discovery.  There are already link technology specific clarifications
   how to tune protocol constants for certain system with the
   expectation to reduce excess Neighbor Discovery Protocol (NDP)
   traffic. 3GPP cellular links are one existing example
   [RFC6459][RFC7066].

   This document specifies updates to the IPv6 Neighbor Discovery
   Protocol [RFC4861] for relaxing the the maximum time allowed between
   sending unsolicited multicast Router Advertisements (RA) from a
   router interface as well as for the maximum router lifetime.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].



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3.  Relationship between AdvDefaultLifetime and MaxRtrAdvInterval

   MaxRtrAdvInterval is an upper bound on the time between the two
   successive Router Advertisement messages are sent, therefore one
   might reason about the relationship between these two values in terms
   of the ratio K=AdvDefaultLifetime/MaxRtrAdvInterval, which expresses
   how many Router Advertisements will be guaranteed to be sent before
   the router lifetime expiry.

   Assuming unicast Solicited Router Advertisements or a perfectly
   stable network, on a theoretically perfect link with no losses, it
   would have been sufficient to have K just above 1 - so that the sent
   Router Advertisement refreshes the router entry just before it
   expires.  On the real links which allow for some loss, one would need
   to use K>2 in order to minimize the chances of a single router
   advertisement loss causing a loss of the router entry.

   The exact calculation will depend on the packet loss probability.  An
   example: if we take a ballpark value of 1% probability of a packet
   loss, then K=2 will give 0.01% percent chance of an outage due to a
   packet loss, K=3 will give 0.0001% chance of an outage, and so forth.
   To reverse the numbers, with these parameters, K~=1 gives 99%
   reliability, K~=2 gives 99.99% reliability, and K~=3 gives 99.9999%
   reliability - the latter should be good enough for a lot of
   scenarios.

   In a network with higher packet loss or if the higher reliability is
   desired, the K might be chosen to be even higher.  On the other hand,
   some of the data link layers provide reliable delivery at layer 2 -
   so there one might even consider using the "theoretical" value of K
   just above 1.  Since the choice of these two parameters does not
   impact the interoperability per se, this document does not impose any
   specific constraints on their values other than providing the
   guidelines in this section, therefore each individual link can
   optimize accordingly to its use case.

   Also AdvDefaultLifetime MUST be set to a value greater than or equal
   to the selected MaxRtrAdvInterval.  Otherwise, a router lifetime is
   guaranteed to expire before the new Router Advertisement has a chance
   to be sent, thereby creating an outage.











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4.  Updates to RFC4861

   This document updates Section 6.2.1. of [RFC4861] to update the
   following router configuration variables.

   MaxRtrAdvInterval MUST be no greater than 65535.  AdvDefaultLifetime
   MUST either be zero (the router is not to be used as a default
   router) or be a value between MaxRtrAdvInterval and 65535.

   As explained in Section 3, the relationship between MaxRtrAdvInterval
   and AdvDefaultLifetime must be chosen to take into account the
   probability of packet loss.

5.  Host Behavior

   Legacy hosts on a link with updated routers may have issues with a
   Router Lifetime of more than 9000 seconds.  In the few
   implementations we have tested with general purpose operating
   systems, there does not seem to be any issues with setting this field
   to more than 9000, but there might be implementations that
   incorrectly (since RFC4861 requires receivers to handle any value)
   reject such RAs.

6.  Security Considerations

   On a link where router advertisements are few and far between, the
   detrimental effects of a rogue router that sends an unsolicited RA
   are greatly increased.  These rogue RAs can be prevented by using
   approaches like RA-Guard [RFC6105] and SeND [RFC3971]

7.  IANA Considerations

   This document does not require any IANA action.

8.  Acknowledgements

   The authors would like to thank the members of the 6man efficient ND
   design team for their comments that led to the creation of this
   draft.  The authors would also like to thank Lorenzo Colitti, Erik
   Kline, Jeena Rachel John, Brian Carpenter, Tim Chown and Fernando
   Gont for their comments and suggestions that improved this document.

9.  References








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9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <http://www.rfc-editor.org/info/rfc4861>.

9.2.  Informative References

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <http://www.rfc-editor.org/info/rfc3971>.

   [RFC6105]  Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
              Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
              DOI 10.17487/RFC6105, February 2011,
              <http://www.rfc-editor.org/info/rfc6105>.

   [RFC6459]  Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
              T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
              Partnership Project (3GPP) Evolved Packet System (EPS)",
              RFC 6459, DOI 10.17487/RFC6459, January 2012,
              <http://www.rfc-editor.org/info/rfc6459>.

   [RFC7066]  Korhonen, J., Ed., Arkko, J., Ed., Savolainen, T., and S.
              Krishnan, "IPv6 for Third Generation Partnership Project
              (3GPP) Cellular Hosts", RFC 7066, DOI 10.17487/RFC7066,
              November 2013, <http://www.rfc-editor.org/info/rfc7066>.

Authors' Addresses

   Suresh Krishnan
   Kaloom
   335 Rue Peel
   Montreal, QC
   Canada

   Email: suresh@kaloom.com







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   Jouni Korhonen
   Broadcom
   Porkkalankatu 24
   FIN-00180 Helsinki
   Finland

   Email: jouni.nospam@gmail.com


   Samita Chakrabarti
   Ericsson
   USA

   Email: samita.chakrabarti@ericsson.com


   Erik Nordmark
   Arista Networks
   Santa Clara, CA
   USA

   Email: nordmark@acm.org


   Andrew Yourtchenko
   cisco
   6b de Kleetlaan
   Diegem  1831
   Belgium

   Email: ayourtch@cisco.com




















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